This invention relates to a monolithic red and infrared wavelength dual laser structure and, more particularly, to a red laser structure and an infrared laser structure side by side laser array where the cladding layers of both the red and infrared laser structures are fabricated from the same semiconductor materials.
Addressable monolithic multi-wavelength light sources, especially laser arrays that can simultaneously emit different wavelength light from different elements in the array are useful in a variety of applications, such as color printing, full color digital film recording, color displays, and other optical recording system applications.
The performance of many devices, such as laser printers and optical memories, can be improved by the incorporation of multiple laser beams. For example, laser printers which use multiple beams can have higher printing speeds and/or better spot acuity than printers which use only a single beam.
In many applications, closely spaced laser beams of different wavelengths are desirable. For example, color printers which use closely spaced laser beams of different wavelengths can overlap the beams, sweep those overlapping beams using a single raster output polygon scanner and a single set of optics, subsequently separate the individual beams using color selective filters, direct each beam onto a separate xerographic imaging station, develop a latent image for each color on a different recording medium, and produce a full color image by sequentially developing each latent image on a single recording medium.
One way to obtain closely spaced laser beams is to form multiple laser emission sites, or laser stripes, on a common substrate. While this enables very closely spaced beams, prior art monolithic laser arrays typically output laser beams at only one wavelength.
Various techniques are known in the prior art for producing different wavelength laser beams from a monolithic laser array. For example, it is well known that a small amount of wavelength difference can be obtained by varying the drive conditions at each lasing region. However, the easily achievable but small wavelength difference is insufficient for most applications.
One method of achieving larger wavelength separations is to grow a first set of active layers on a substrate to form a first lasing element which outputs light at one wavelength, and then to grow a second set of active layers next to the first to form a second lasing element at a second wavelength.
Side by side monolithic laser arrays can not only output closely spaced laser beams of different wavelengths, but beneficially the output laser beams are aligned and their polarization axes are parallel or perpendicular to the lines joining the two lasers.
In printing systems applications, the requirements for red/ir side by side laser structures are (1) accurate lateral spacing of 50 microns or less with zero or minimum vertical spacing between the side by side laser structures, (2) the red and IR laser structures, although closely spaced side by side, are independently addressable, (3) low thermal or electrical crosstalk between the side by side laser structures, (4) a single transverse mode for light emission from both the red and IR laser structures, (5) fast switching of less than 3 nanoseconds and (6) long lifetime for the red/ir side by side laser structures.
It is an object of this invention to provide side by side red/ir laser structures in a monolithic structure capable of outputting closely spaced, multiple wavelength laser beams.